The effects of metsulfuron-methyl on injury and acetolactate synthase (ALS) activity were measured in immature oil plam seedlings under greenhouse conditions. Metsulfuron-methyl sprayed directly onto seedlings caused a whole range of injuries to the 18-month-old palm seedlings, but its residue in soil did not affect seedling growth. Chlorosis appeared three weeks after treatment (WAT). The percentage of injury score was found to increase proportionally with herbicide dosage. Metsulfuron-methyl inhibited ALS enzyme in the seedlings. Metsulfuron-methyl at 41nM could inhibit 50% activity (I₅₀) of ALS enzyme. Metsulfuron-methyl compound was metabolized to seven metabolities, of which two could not be identified